Social networks and communities are increasingly introducing location as an input to their services, e.g. showing the position of your buddies in a map or sending alerts when a buddy is near you. There are also community games in which location plays an essential role, e.g. geo-caching, a treasure hunt where you have to seek hidden containers. Besides, others services such as the ‘virtual post-it’, a message tied to a location that is visible only for those reaching that location, have already been suggested. The current problem lies in finding a perfect technical solution to enable this zone-centric messaging, because the existing solutions are neither scalable, accurate nor available to all devices.
The existing solutions are basically of two types:                Relative positioning, consisting in detecting the proximity of users via a short-range radio, especially Bluetooth® or WiFi. This requires the deployment of a local box but provides high accuracy.        Absolute positioning, using an absolute positioning method (e.g. GPS, cellular) that compares the user position with the geographical area of the target zone, detects the event of entering there, and then, triggers the delivery of messages to the device through the cellular channel. This solution does not require the deployment of a local box.        
The existing relative positioning methods, based on Bluetooth or similar short range radio technologies, have a number of known drawbacks: not all mobile phones have the Bluetooth hardware, not all have it active (especially for saving battery), the discovery time can be high and the number of concurrent connections is low (generally only seven). Regarding the absolute positioning methods, the ones based on the cellular network are not accurate enough (cell resolution) and require a continuous polling or tracking of user's position that consumes network resources; and the ones based on the terminal (GPS) do not work indoors and require an internal process (local tracking) that consumes battery.
It is well-known that abbreviations and acronyms are frequently used in the mobile telephony field. Below is a glossary of acronyms/terms used throughout the present specification:
3GPP The 3rd Generation Partnership Project
BSC Base Station Controller
BTS Base Transceiver Station
GPS Global Positioning System
GSM Global System for Mobile Communications
HTTP Hyper Text Transfer Protocol
IMSI International Mobile Subscriber Identity
IP Internet Protocol
MAC Medium Access Control
MMS Multimedia Messaging Services
MSISDN Mobile Subscriber Integrated Services Digital Number
MSC Mobile Switching Centre
LAC Location Area Code
RNC Radio Network Controller
SGSN Serving GPRS Support Node
SMS Short Message Service
TIMSI Temporary International Mobile Subscriber Identity
UMTS Universal Mobile Telecommunications System
WAP Wireless Application Protocol